Cannabidiol (CBD) has a variety of pharmacological benefits, including, but not limited to anti-inflammatory, analgesic, anti-convulsant, anti-psychotic, anti-fibrosis, anti-scarring, anti-oxidant, neuroprotective, anti-infective, anti-cancer and immunomodulatory effects.
Cisplatin is a common chemotherapy used to treat a variety of cancers. Unfortunately, cisplatin has a dose limiting effect wherein 50-85% of patients develop peripheral neuropathy 3-6 months into treatment. Cisplatin-induced neuropathy (CIN) presents in a “stocking and glove” distribution causing tingling paresthesia, numbness, and allodynia (Paice, 2010; Amptoulach et al., 2011). Pain management for CIN includes anticonvulsant, antidepressant, and non-steroidal anti-inflammatory drugs. These drugs prove to be well tolerated in patients but show little efficacy in treating CIN (Wolf et al., 2008; Amptoulach et al., 2011; Miltenburg et al., 2014).
While opioids can provide effective CIN pain relief, 76-96% of patients report aversive side effects that include sedation, nausea, and fatigue which limit usefulness and diminish patient quality of life (Guindon et al., 2008; Toth & Au, 2008). Added concerns of opioid therapy include tolerance, dose escalation, and dependence that can lead to withdrawal symptoms upon CIN resolution (Kim et al., 2015). Collectively, these observations suggest a need to develop novel pharmacotherapies for CIN.
Cannabinoids (CB) are used in oncology settings to control nausea, weight loss, lack of appetite, and chemotherapy related pain (Alexander et al., 2009). CB analgesia in both chronic and acute pain models is mediated through CB1 and CB2 receptors that are differentially expressed in the central and peripheral nervous systems (Chiou et al., 2013; Pisanti et al., 2013). An emerging body of literature supports the notion that CB systems may also modulate CIN. For example, CB1 and CB2 direct and indirect agonists attenuate tactile allodynia in rodent models of CIN (Vera et al., 2013; Guindon et al., 2012, Khasabova et al., 2012). However, like non-opioid therapies, CB compounds have modest efficacy and are of limited usefulness.
CB1 and opioid receptors are co-localized in pain pathways. Evidence suggest a dual pharmacotherapy at these targets may increase CB-mediated analgesic effects (Wilson-Poe et al., 2008; Hall et al., 2005; Mansour et al., 1988; Basbaum et al., 1984). For example, the CB1 agonist THC shows synergistic effects with sub-analgesic doses of the mu opioid agonist morphine in a rat arthritic pain model (Cox et al., 2007). However, use of any CB1 agonist in oncology settings is unlikely due to these compounds increasing the proliferation and growth of some tumor cells (Hall et al., 2005). Interestingly, other CB constituents that show low affinity to CB receptors also show synergistic effects with low dose opioids. For example, cannabidiol (CBD) shows synergistic effects with sub-analgesic doses of morphine in an acute pain model (i.e., acetic acid writhing) but not against thermal pain (Walker et al., 2015). Whether a combined CBD-opioid pharmacotherapy could provide highly efficacious pain relief against cisplatin neuropathy is unknown.
Challenges in pain management in oncology settings lead to unnecessary suffering, diminished quality of life, and in some instances, decreased life expectancy due to patients forgoing continued chemotherapy treatment. Current therapies against CIN are either only modestly effective or are fully effective but poorly tolerated.